Most conduits such as pipelines, tubulars, lines and ducts that carry fluids need to be “pigged” at certain times. This is accomplished by inserting a pig into the conduit at a first point and allowing a driver, such as the force of fluids flowing through the conduit, to move the pig through the conduit to a second point where it is caught and removed from the conduit.
Some pigs perform a maintenance or operational pigging function, e.g. cleaning, —such as scraping of solids from the interior of the conduit; swabbing—such as removing liquids or gases from the conduit; batching—such as separating different fluids in the conduit, etc. Some pigs monitor and convey information about a particular condition or performance of the conduit.
Such pigs include extensions of body material to ride against the interior surface of the pipe through which they are conveyed. Body extensions may include foam, rubber seals, bristles of a brush-like structure, etc. Such extensions may act to create a barrier in the conduit for harnessing fluid pressure or dividing two types of fluid and/or may contact the conduit inner wall to measure a wall parameter, provide electrical or magnetic contact between the pig and the wall, centralize the pig in the conduit or scrape against the walls.